1. Field of Invention
This invention relates to structures including microvalves. This invention further relates to methods of forming the structures.
2. Description of Related Art
Known ink jet print heads include a heater wafer, a channel wafer and an ink reservoir. Ink channels and nozzles are formed in the ink jet print heads for flowing and discharging ink onto recording media. Heating elements are provided in the ink channels to heat the ink and cause ink droplets to be discharged out of the nozzles and onto recording media.
FIG. 1 illustrates a known ink jet print head 10 structure. The ink jet print head 10 comprises a device wafer (or heater wafer) 12 and a channel wafer 14 over the device wafer 12. A bonding layer 15 is formed between the device wafer 12 and channel wafer 14. An ink reservoir 16 contains a supply of ink. The ink is supplied from the ink reservoir 16 to a plurality of ink channels forming nozzles. A single ink channel 18 is shown for simplicity. The ink channel 18 extends to the front face 20 of the ink jet print head 10. A heating element, such as the heating element 22, is formed on the top surface 24 of the device wafer 12 for each ink channel 18. The heating element 22 is powered to heat the ink in the ink channel 18. Heating of the ink by the heating element 22 forms vapor bubbles in the ink channel 18. A vapor bubble 26 is shown formed over the heating element 22. The vapor bubble 26 pushes ink through the ink channel 18 in the direction toward the front face 20. The ink is ejected as ink droplets 28 onto a recording medium (not shown).
The vapor bubble 26 formed by heating the ink in the ink channel 18 also pushes ink through the ink channel 18 in the direction toward the ink reservoir 16. Gas bubbles 30 formed by heating the ink can also flow back into the ink reservoir 16. The gas bubbles 30 can agglomerate and grow in the ink reservoir 16 to a point at which the gas bubbles 30 affect the printing performance of the ink jet print head 10.
This invention provides structures including microvalves that can be used in various devices that comprise fluid channels to control fluid flow in the fluid channels. Structures that can be formed according to this invention can be used, for example, in ink jet print heads to overcome the above-described problems of known ink jet print heads, such as those described above for the ink jet print head 10.
This invention separately provides ink jet print heads including microvalves.
This invention also separately provides methods of forming structures including microvalves.
This invention also separately provides methods of forming ink jet print heads including microvalves.
Exemplary embodiments of structures according to this invention comprise a first substrate and a second substrate defining a fluid channel. The fluid channel includes a first channel portion and a second channel portion. A heating element is provided in the first channel portion. The heating element heats fluid disposed in the first channel portion to form vapor. A microvalve is formed on one of the first substrate and the second substrate. The microvalve includes a flap that is flexed by pressure exerted on the flap by the vapor on the fluid to at least substantially prevent, or even completely prevent, the fluid from flowing from the first channel portion into the second channel portion.
The structure can be, for example, an ink jet print head. The microvalve can at least substantially prevent, or even completely prevent, gas (from bubble nucleation) from flowing into the ink reservoir and affecting printing performance.
Exemplary embodiments of methods of forming the structures according to this invention comprise forming a thermal oxide over a silicon substrate; forming an opening through the thermal oxide; doping the silicon substrate with boron via the opening in the thermal oxide to form a boron-doped region in the silicon substrate; forming an n-type dopant region in the boron-doped region; etching the boron-doped region to form porous silicon; oxidizing the porous silicon to form silicon dioxide; and etching the silicon dioxide to form a channel in the silicon substrate. The n-type dopant region forms a flap of the microvalve.